Add start of a sourceview list

This shows in a separate window for now, so we don't
mess up the xibs. Once I'm satisfied with the result,
I can put it into the main view with a single change :)
Sidebar: populate with branches

This is far from perfect, but should indicate
which direction this is going in
SideBar: Add branches as children

This makes a nice tree, which should be more
readable than the existing list. The local
branches are expanded by default.
Sidebar: display a custom icon

These are based on a contribution by Vincent Esche,
but we'll probably have to change them a bit.
Sidebar: hook up branch switching

This is far from perfect, but at least you can
use it to navigate the stuff a bit now :)
Sidebar: Handle selection changes
SideBar: Add ViewAction and ViewRemote objects

These two new classes can represent items in our SourceList
that refer to specific actions (such as comitting), or
specific Remotes.
Sidebar: Add "Commit" action

When this tree leaf is selected, the view switches
to the commit view.
WIP: Move the sidebar to the history view instead

I'm not sure what we should do with the commit stuff, but
this seems more reasonable
Don't show the Actions menu for now
PBGitRevSpecifier: tweak "isSimpleRef" a bit

For example, HEAD is a simple ref, but "stable..HEAD" isn't.
Sidebar: Check if we have enough path components
Sidebar: add a new ref if it can't be found
Update Sparkle Framework
Add update key
CommitView: edit the xib a bit

This thing crashed when switching to the commit view in a WebKit private method.
After resaving, it worked again. Not very confidence inspiring :(
Merge branch 'pu/pb/newSparkle' into stable

* pu/pb/newSparkle:
  Add update key
  Update Sparkle Framework
Add release notes for 0.7.1
Info.plist: No longer use the LONG_VERSION hack

Since 0b81911d we have a nicer Git version we can use, so we no longer
require this hack. It also interferes with Sparkle's updating system,
so just remove it and use the same versioning system as we use for
the short string.
Remove Sparkle feed url changer

Apparently the setFeedURL: method is persistent, so if someone ever used
a nightly, it would keep the debug URL. That's not what I intended (I wanted
to use a different URL for debugging purposes), so let's just remove it.